Some medical devices, including for example vessel occlusive devices (e.g. artificial urinary, bowel or esophageal sphincters), tissue expanders, or breast implant, may require some parts to be filled with liquids for proper operation. A liquid filling process of the medical devices can be performed just before application. For example, a vessel occlusive device may be filled with a desired amount of saline solution before implanting the vessel occlusive device in a human body.